Method for the production of formaldehyde



Sept. 9 J. 1.. HALL 2,384,028

METHOD FOR THE PRODUCTION OF FORMALDEHYDE Filed Oct. 22, 1942 kick/1). Hall Patented-Sept. 4, 1945 UNITED. STATES PATENT orncs wsamnr or a,

John l... mu, Charleston, w. Va. Application October 22, 1942, Serial No. 402,984 scam. (erase-e04);

This invention .relates to improvements in methods of making formaldehyde, and, more particularly, to a process involving partial oxidation or combustion of natural gas or methane at substantially atmospheric pressures.

Hitherto, methods have been proposed for the formation of formaldehyde by the incipient, partial combustion of methane at pressures of 250 lbs. per sq. in., and above. The emciencies of such processes have been very low, due to the fact that in the combustion of methane decomposition takes place rapidly at and above a temperature of 900 F., so that the resulting products have been mainly carbon dioxide and water with lesser amounts of carbon monoxide and minimum understanding of the invention and the novel means devised to effectuate the same, the low temperature combustion of methane may be 11- lustrated by the following equation:

At medium temperatures the reaction proceeds further and the breakdown of the formaldehyde formed and the formation of carbon monoxide, 00. Upon carrying the combustion at a higher temperature the end products will be carbon dioxide and water. The optimum temperature will be below 900 F., although temperatures of 1050 to 1200 F., may be used providing timeof contact in the flame is held below 15 sec. per cubic foot of air. The reaction may be operated to yield up to 16 pounds of formaldehyde per thou,- sand cubic feet of methane burned, although a yield of 8 pounds of formaldehyde per thousand cubic feet of methane has been found to involve the least operative difllculties.

The feature of novelty which appears to be controlling in the present case is the exact and determined quenching of the reaction flame at the appropriate point. Thus,'when a methane flame is burned in air under conditions such that it is blownby a blast of air, it is "found that the formaldehyde is formed at the inner cone, while The semi-circular babies carbon monoxide and carbon dioxideare respec 5s tively formed forwardly toward the tip of, the

flame inthe region of increasing available oxygen.

Thus, atthe extreme tipof: the flame, where maximum oxygen is available, the reaction product is carbon dioxide. At-the innermost point of the flame, where minimum oxygen ispresent, the desirable yield-of formaldehyde is evident. By a careful adjustment and control of quenching liquid it has been, found possible to secure maximum yields of formaldehyde.

The method and means for securing the desirable results of the present invention will be described more particularly with reference to the accompanying sheet of drawings, in which isillustrated, partly in vertical section and partly in elevation, a combustion chamber and scrubbing tower with recycling means for recovering the formaldehyde liquor obtained. t

Referring more particulary to the drawing the apparatus comprises a combustion or furnace unit III, a scrubber 20, and a battery of coolers 30 and II. The furnace may comprise a brickwork chamber ll, having an air chamber or blower box I2, fltted with a plurality of aligned apertures l3, positioned above the center line of the front wall of the chamber. An air inlet pipe I of any suitable construction and having the usual controls will feed-air to the chamber 12. The front part or combustion chamber of the furnace designated by the numeral II has a liquid-proof liner orcontainer It at the bottom thereof, a top outlet or gas passage l1, and a bottom liquid passage ll, both entering into the bottom chamber 2!, of scrubber tower ii. The combustion chamber I5 is flttted with. the gas combustion mechanism and comprising a plurality of burner pipes I fed by a gas main 2 and protected by semi-circular baflies or air guards 3. The height of the burner tubes l is so arranged that the flames 4 are normally'pcsitioned at the height of the air-ports or apertures it. lare so arranged as to have the rear or arcuate sections thereof immediately facing the air-ports I3, with the result that, with the flame ignited and air blowing through the ports II, the battle directs the air current around and in front of the flame, causr and adjustment of the same.

, of nozzle 5 to any desired point to assure quenching of the tip of the flame at the exact point where maximum formaldehyde production is assured. A valved ignition port I! may be provided in the top of the furnace chamber above the pipe I, and, where a plurality of burners are installed, there will be a corresponding number of ignition ports and peep-holes l9a which permit close examination of the flames and the progress of the combustion reaction, and also permit accurate adjustment of the spray heads or quenching nozzles 5 to insure correct calibration The pipe 3 may be provided with a flow of water from the cooler unit 30, and the reaction products are dissolved and brought from a temperature of about l200 down to a temperature of 300! into the bottom of the chamber. Here the temperature may decrease further to 200. The amount of liquid permitted to accumulate in the bottom of the furnace and the scrubber tower, which, as shown, are pr( vided with a connecting port l8, will be determined by the liquid level control 22 at the bottom of the scrubber. The scrubber may be conventional in structure and comprise a plurality of bubble units 23 and the top exit pipe 24 through which fixed and insoluble gases and vapors such as nitrogen and C0, are withdrawn. The scrubber has an outlet pipe 25 at the bottom and an inlet pipe 26 below the top plate of the column. The outlet 25 is provided with a valved draw-oil 26 to permit cleaning out of the unit where desired. However, this element is usually closed and free connection is provided with pipe 21 opening into the lower cooler unit 3| of the cooler battery 30. The aqueous formaldehyde solution is drawn from chamber 2i of the scrubber through pipe 21 and through cooler 3| by pump 32 and delivered thence to pipe 33 to the upper cooler unit 30. From this unit the products are'delivered through pipe 35 to inlet 26 of the scrubbing tower or by-passed through pipe 8 to the spray or quenching units 5, the amount of quenching liquid being delivered being determined by the operation of the valved inlet pipe 6. The outlet line 35 of the cooler unit is provided with a draw-off line 36 controlled by valve 31 and terminating in a drawoff line. The valve 31 is directly controlled by any suitable mechanism such as linkage 39 operated by liquid level control 22. By this means the height of liquid in the bottom of the scrubber chamber 2| and the bottom l3 of the combustion chamber, which is in fluid communication therewith, is readily maintained. Thus,

when the level of liquid rises above the desired point the excess is pumped out of the system let element 02 for the coolant. It will be noted that the pipe or connection ll serves the dual function of outlet for unit 30 and an inlet for unit 3i. By the arrangement shown the maximum'cooling eflect is delivered to the products liberated from the last unit of the cooling battery, and the incoming hot materials are treated by the eiliuent coolant which is appreciably hotter than the eilluent coolant.

From the above it will be seen that by the simple control of the duration of the combustion of methane in an oxygen flame the time of combustion'can be restricted to less than 15 sec. and preferably to about one-quarter sec. per cubic foot of gas. Closer control will give high yields of formaldehyde, the i6 poundsyield per thousand cubic feet of methane being discussed above. Even with the average yield of 8 pounds per cubic foot of methane there is an appreciable margin of unexpected efllciency over current processes, which give only a few pounds per thousand cubic feet of gas.

In the apparatus described above, it will be seen that by constantly recycling the aqueous formaldehyde as fast as it is formed and usin it as the quenching medium, there with be a constant build-up or saturation of the medium with formaldehyde, so that maximum concentrations may be built up in the system before any of it is withdrawn through delivery pipe 33. This permits further efficiencies in the operation of the process by reducing the amount of concentration required to secure high strength formaldehyde liquors or pure formaldehyde gas. By constantly using this fortified liquor as a scrubbing medium for any gases not entrained by the quenched liquor, complete recovery of all formaldehyde is assured and also the complete elimination of inert gases and other gases and vaporous products of reaction. This rapid and complete withdrawal of materials from the system increases the speed of the combustion reaction and causes it to progress rapidly to the right, due to the absence of any inhibiting factors or products.

From the above it will be seen that a novel process and apparatushave been disclosed for the making of formaldehyde by the partial combustion of methane and relatively great excess of oxygen or air which also acts as a coolant and under determined and controlled conditions of time and amount of combustion permitted, so that the optimum formaldehyde-forming reaction is closely controlled and maintained, and the products of reaction substantially instantaneously withdrawn from the reaction sphere and cooled below the decomposition point, and then subsequently cooled further, aliquot portions being used to determine the desired quenching of undesired reactions without introducing extraneous or foreign materials into the reaction chamber.-

I claim:

1. The method of forming formaldehyde from methane comprising burning methane in a great excess of air with an elongated flame and continuously quenching the tip of the flame.

2. The method of forming formaldehyde from methane comprising burning methane in twenty times its volume of" air with an elongated flame and continuously quenching the tip of the flame.

3. The method of forming formaldehyde by the 7 partial combustion of methane, comprising burning methane in a twenty-fold excess of oxygen at temperatures of 1050 to 1200' 1". with an elongated flame and continuously quenching the tip of the flame.

4. The method of forming formaldehyde by the partial combustion of methane, comprising buming methane in a twenty-fold excess of oxygen at temperatures of 1050 to 1200" R, with an elongated flame and for a time period of onequarter second to flfteen seconds and continuously quenching the tip of the flame with a liquid quenching medium.

5. The method of forming formaldehyde by the partial combustion of methane, comprising buming methane in a twenty-fold excess of oxygen at temperatures of 1050 to 1200 F., with an elongated flame and for a time period of onequarter second and continuously quenching the tip of the flame with a liquid quenching medium.

6. The method of producing formaldehyde by incipient partial combustion of methane in a twenty-fold excess of oxygen, including elongating the reaction flame and subjecting the elongated flame to determined spatial quenching with recycled products of the reaction in an aqueous solution.

7. Method according to claim 6 in which the spatial quenching of the flame is carried up to the point ofmaximum formaldehyde formation at the innermost cone of the flame.

8. Method for the production of formaldehyde by incipient partial combustion of natural gas in a twenty-fold excess of air, comprising burning methane in a current of air under conditions such as to produce an extended flame, directing a quenching medium at the flame and adjacent the inner cone of maximum formaldehyde formation, to preclude pyrolysis of the formaldehyde formed in the advanced tip of the flame, withdrawing the formaldehyde and quenched liquor through a cooling system, and passing the cooled products in counter-current to flxed gases from the reaction, and withdrawing as a product aliquot portions of the recycled formaldehyde gas-fortifled liquor from the cool end of the cooling units.

9. The process of preparing formaldehyde from natural gas, comprising subjecting a thousand cubic feet of natural gas to incipient partial combustion in a twenty fold atmosphere of oxygen positively elongating the flame, and limiting the period of combustion to one-quarter to fifteen seconds to give a yield of 7 to 16 pounds of formaldehyde and continuously quenching the tip of the flame with a liquid quenching medium.

JOHN L. HALL. 

